Tony: Thanks for responding to my post. I hope I hear from others also. Regarding hygrometer placement, I have placed it at various locations under the soundboard, but always on top of one of the beams (at most 1 cm below board) AND I have actually put the darn thing right on top of and next to (actually touching) the humidistat. I have placed up to three different hygrometers under the piano at the same time (the three were compared at stable conditions and are known to produce similar RH readings) and get the results I have described. As far as the Rule of Thumb goes, yes I agree that they are just generalities, but they should be based in reality. My observations suggest that a reduction in RH of 1% for each 1 Watt is way off the mark - even in a vertical (where presumably the system would be at maximum efficiency). My vertical produced results closer to a 1% RH reduction for every 3 Watts (I suppose a grand would be even less efficient). Regarding your question about actual moisture content of the wood: The various species of spruce commonly used in soundboard construction have physical properties that fall within a certain limited range. This includes the typical relationship between moisture content of the wood and the RH of its atmospheric environment. This relationship will remain constant. Experimentation has established that RH around 42% produces the most desireable moisture content for spruce soundboards (what is that MC?). Because of the known relationship between spruce and atmospheric RH, RH in the soundboard environment will provide an accurate (although indirect) indicator of soundboard moisture content. Terry Farrell Piano Tuning & Service Tampa, Florida mfarrel2@tampabay.rr.com ----- Original Message ----- From: "Tony Caught" <caute@accessnt.com.au> To: <pianotech@ptg.org> Sent: Wednesday, February 02, 2000 6:56 AM Subject: Re: Dampp Chaser or not, that is that question! > Hi Terry > I will try to answer some of your questions but maybe the manufacturer can > answer them better. I am involved in this discussion because I believe that > Dampp-Chaser is the best available until a system is introduced that > operates on moisture content of the timber. > > > I would like to hear from others about DC dehumidifier system designs & > > installations. > > > > I live in Florida where most homes are air-conditioned, and relative > > humidities (RH) range from a low of approximately 35% to perhaps 80%. I > have > > a 5' 10" Boston with the DC unit installed. I have monitored it for months > > and it turns on when the RH reaches approximately 68% and turns off when > it > > reaches about 46%. I just checked it now and the unit is off and the RH is > > 59% @ the soundboard bottom. Clearly, this is not functioning as the > > manufacturer advertises. > > The manufacturer designed the system to to monitor the humidity at or very > close to the heating bar to ensure that the heat does not stay on too long. > Heat rises, it is possible that if you took the measurements at the top of > the piano instead of the bottom, you would have different readings. > Possibly also if you measured the RH at the bar it would be different again. > The RH measuring devise is inside the humidistat very close to the bar. > > Sorry there I am talking about an upright not a grand. > > I have 200W under my piano and when the room is 75% > > RH, it is on approximately half the time to maintain the soundboard > > environment in the 46% to 68% RH range. > > > > I believe in the philosophy of putting a substantial amount of wattage > under > > the soundboard to enable lowering the RH to the 40% range under humid > > conditions. I have observed that one needs to raise the temperature > > approximately two degrees F for every three percent reduction in RH. Thus, > > to reduce the RH in the area of a soundboard in a room that is 80 degrees > F > > and 70% RH, the soundboard area needs to be heated to a temperature of 100 > > degrees F to reduce the RH to 40%. > > > > >From a previous post (below in its entirety): > > >"....today the temp was 33 Celsius and 90% humidity. Now if I > > was to install a D-C with 50 watts of heat it would bring the RH in the > > piano down to 40% (rule of thumb 'for every watt of heat you remove 1% of > > humidity') but that would mean that the heat would remain on constantly > and > > that in turn may cause considerable damage to the piano...."< > > > > How on earth is a 50W rod going to pull RH down to 40%? Where does such a > > rule of thumb come from? The grand installations that I see are usually > only > > 50W. You should be able to put a ridiculous level of wattage under a piano > > with no damage because the humidistat will turn it off. > > Rule of thumb ? A very basic guide when talking to customers to describe how > much heat you have to put into a piano to cover a certain RH level. Tis not > an exact science but easy understood and fairly close to the mark. Also if > measurements are taken in an upright piano where all devises are inclosed in > their own enviorment you will get one reading whilst in a grand piano the > devises are open to the room atmosphere and breezes no mater how > gentile,thus you will get different measurements. > > > > I formerly had a 46" vertical piano that I put a 50W rod in. The rod would > > raise the temp about 12 degrees F max for a drop in RH of approximately > 18%. > > So, if the room was 75% RH, my piano interior was about 58% RH. Better > that > > room RH, but my clients are not getting what they are paying for and think > > they are getting. > > > > I would like to know where the data used in the graphs in the DC brochure > > comes from. That graph has room air going up to 95% RH and the piano > > interior staying below 45% RH. That means that the piano interior would > have > > to be heated to a temperature about 33 degrees F above the room temp. How > > many watts is required to KEEP the piano at say about 115 degrees F for > the > > summer? > > > > What are others' thoughts on this. I would really like to hear from others > > how many watts they put under a mid-sized grand, and if anyone else has > > monitored the system's effectiveness, i.e. what are the turn-on RH and the > > turn-off RH, and what percent of the time is the system energized. > > > > Thanks, I feel better now. > > I understand how you feel, I am always confused as to what is right and what > is not. It seems logical that the true guide line should be moisture > content of the timber and not the RH. I say this because at a temp of 24 > Celsius and a RH of 42% you will have a set reading for moisture content, > but if you increase the temp to 32 Celsius at the same RH of 42% youe have > to have a lower moisture content in the timber. > > does anyone know the correct formula to work this out. ??? > > Tony Caught IC PTG Australia > caute@accessnt.com.au > > > > > Terry Farrell > > Piano Tuning & Service > > Tampa, Florida > > mfarrel2@tampabay.rr.com > > > > ----- Original Message ----- > > From: "Tony Caught" <caute@accessnt.com.au> > > To: <pianotech@ptg.org> > > Sent: Tuesday, February 01, 2000 8:20 AM > > Subject: Re: Dampp Chaser or not, that is that question! > > > > > > > John > > > > > > If you were in the tropics, yes I would go for the 55% humidity bar, but > > you > > > are not. > > > What you have to remember is that their are two factors that control the > > > moisture content of the timber in the soundboard (piano), humidity and > > > temperature. > > > > > > I have a copy of the moisture content of various timbers as registered > > with > > > the CSIRO that cover most of Australia. > > > > > > You will find that in Newcastle the moisture content for Radiata Pine is > > > very stable, varying 1 degree only from 15% to 16% with the average of > > 16%. > > > Sydney, for the same timber in the same thickness (1/4") varies between > > 13% > > > and 16% with the average of 14%. > > > Melbourne goes from 12% to 17% with an average of 14%. > > > > > > Parramatta being further inland (not much but further) than Sydney, a > > little > > > less humid, thus you could expect the moisture content to be lower. > > > > > > Pianos in general are made with a moisture content in the soundboard of > > 8%. > > > This 8% is expected to increase to say 12 or 13% to increase crown etc. > > but > > > that is another story. My point is that with your lower average > > > temperatures, you require a lower humidity level in the soundboard. Go > > for > > > the standard 42% humidity Dampp-chaser system, it will give you a better > > > sound. > > > > > > Here in Darwin, today the temp was 33 Celsius and 90% humidity. Now if > I > > > was to install a D-C with 50 watts of heat it would bring the RH in the > > > piano down to 40% (rule of thumb 'for every watt of heat you remove 1% > of > > > humidity') but that would mean that the heat would remain on constantly > > and > > > that in turn may cause considerable damage to the piano. > > > However the moisture content of the same timber in the tropics for Cape > > York > > > are 17% to 21% with a mean of 19%, thus a tropical or wet humidistat of > > 55% > > > H was developed to ensure that the heater was not on all the time and > that > > > the piano moisture content was not reduced too much more than the lowest > > > level of moisture content. > > > > > > Stick with the standard 42% is ideal around that area. > > > > > > Tony Caught IC PTG Australia > > > caute@accessnt.com.au > > > > >
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